Looks like you’ve probably installed a previous version of postgresql at some point, which at the time was referenced via homebrew/versions/postgresql91, but the new hotness is versions are now a part of homebrew/homebrew-core. This changed as part of Homebrew 1.2.

Your best bet, assuming that you probably just want the latest versions of these things, is to brew reinstall postgresql and psqlodbc. This is outside of the scope of homebrew however.